The intestines are the main digestive organ of the human body, and also play an important role in our immune system. The species of bacteria found in the intestines are diverse, with both beneficial and undesirable bacteria present. Many relevant studies have shown that an increase of probiotic bacteria in the intestines induces beneficial effects on human health, such as preventing the growth of undesirable bacteria, improving intestinal peristalsis, enhancing immunity, and preventing cancers (Gibson and Roberfroid, 1995). Moreover, studies have shown that the intestinal bacteria also help control the metabolism of fats. Whenever the intestinal microbiota is out of balance, it generally leads to low-grade chronic inflammation throughout the human body, which consequently increases the occurrence of obesity and metabolic disorders (Cani and Delzenne, 2009). Therefore, the intestinal bacteria are of vital importance to the human body. Generally, the intestinal microbiota may be improved by the intake of health supplements, which can be divided into the following three categories: probiotics, prebiotics, and synbiotics, which is the combination of probiotics and prebiotics.
Soybean oligosaccharides are common prebiotics; a naturally occurring soybean oligosaccharide is consisted of raffinose and stachyose. It is a sweetener that is low in sweetness and calories, and can be used as a substitute for sucrose in functional foods or low-calorie foods. Because it does not induce the secretion of insulin after intake, the diabetes patients can consume it without concerns. The main components of the soybean oligosaccharides are not absorbed in the intestines, but utilized in the bowel section, where the majority of the bacteria flora is present. Relevant studies have shown that harmful bacteria like Escherichia coli cannot utilize the oligosaccharides, and its growth is suppressed instead. In addition, soybean oligosaccharides are fermented or partially fermented in the bowel to produce metabolites like short chain fatty acids (SCFA), acetate, propionate, and butyrate, which directly promote intestinal peristalsis and facilitate the passing of wastes. Acetate or butyrate are known to inhibit the growth and reproduction of harmful bacteria, which helps change the intestinal microbiota and make the intestines an ideal environment for the beneficial bacteria to multiply.
Generally speaking, the term probiotics is thought to be referring to bacteria only. But recent discoveries have indicated that the active substances derived from some of the probiotic bacteria also help promote the health of the host. Therefore, the term probiotics is now used to refer to the extracts of viable, dead and resident bacteria, as well as metabolites thereof Lactic acid bacteria are known to possess a number of biological functions and can be safely consumed by humans, thus making them an important material in the development of health supplementary products.
Lactic acid bacteria are considered the most significant group of bacteria in the category of probiotics, as the humans have a long history of consuming fermented dairy products, which means the lactic acid bacteria are generally safe to be consumed, and regarded as a best example of beneficial bacteria in human intestines. When lactic acid bacteria enter the intestines, they subsequently stimulate specific and non-specific immune responses from lymphatic tissues thereof, and the responses are affected by how well the bacterial bodies come into contact with the lymphatic tissues in the intestinal cavities. The lactic acid bacteria are thought to be effective only when they adhere to the intestines and reproduce. And some experiments showed that after stopping consuming lactic acid bacteria, the bacteria disappear within a few weeks and do not remain in the intestines. However, even short periods of adherence led to stimulations of the intestinal immune system, which was true even in patients who were taking antibiotics or suffering diarrhea. The intake of lactic acid bacteria helped re-establish the intestinal microbiota in the patients and restore the balance of the immune system. The lactic acid bacteria are therefore useful for treating intestinal disorders and inflammation, as they can promote the internal defensive mechanism and improve intestinal microbiota in the host. Past researches had indicated that the earlier a person consumes the lactic acid bacteria, the more likely it is for the bacteria to interact with the cell receptors of the host, and then the bacteria can establish themselves on the epithelial cell mucus layer to become symbiotic bacteria in the gut (Parvez et al., 2006). As the lactic acid bacteria play a critical role in determining the intestinal health of its human host, products based on the lactic acid bacteria or derived therefrom has become increasingly popular on the market (Chen et al., 2007). Currently, the commercial lactic acid bacteria products are most commonly based on probiotic bacteria strains like Lactobacillus sp., Bifidobacterium sp., as well as Lactobacillus plantarum (Parvez et al., 2006).
One of the common methods for fabricating synbiotics is to add probiotics into prebiotics, as disclosed in Japanese Patent No. JP2-200168, in which a lactic acid beverage is produced by using the saccharides-containing soybean steepwater resulted from the processing of soybean to make bean curd. However, the method uses only water to extract the soybean steepwater and fails to remove the particular odor of the soybean, and the resulted extracts are limited in volume, which is not cost-effective. Other methods had also been proposed to make synbiotics by adding probiotics (such as lactic acid bacteria) into prebiotics (such as soybean oligosaccharides), as seen in the Korean Patent No. KR 20020043078, which disclosed a composite probiotic, and in the Chinese Patent No. CN 101406489A and CN 101496583A, which disclosed a composite microbial inoculant and fabrication method thereof, and a nutritional food containing probiotics, respectively. The methods from the three patents fabricate the synbiotics by adding selected lactic acid bacteria composites into soybean oligosaccharides at specific ratios, but the composition of the soybean oligosaccharides are not defined clearly. Moreover, the amount of raffinose and stachyose are not described in any ways, but they are important in the selective replication of the intestinal bacteria. In addition, a method for fabricating extract liquids from fermented soybean was disclosed in the Taiwan Patent No. 252759; after obtaining soybean extract liquids by dissolving it using hot water, the liquids are added with lactic acid bacteria for further culturing, and then immune-regulating active substances are obtained by heat-sterilizing and filtering the fermented liquids, which are prebiotic substances only.
From the above examples we know that the current methods for fabricating synbiotics are still based on the addition of probiotics into prebiotics. Therefore, the inventors of this invention had proposed a method of inoculating probiotics into prebiotics to facilitate fermentation, and then directly using the fermented product as the synbiotics in response to the previous issues.